Optical encoders are a versatile means of detecting motion. Optical encoders are used in industrial and agricultural machinery, as well as office equipment to detect linear and rotary motion and position. Typically, optical encoders have a disk or a plate containing opaque and transparent areas, called the code strip. The code strip passes between a light source (e.g., an LED) and a detector to interrupt the light beam from the light source. The resultant flickering is a signal which is received by photodiodes on a detector, and converted into electronic signals. The electronic signals that are generated are then fed into a controller where position and velocity data are calculated based upon the signals received. The light from the light source must be fully transmitted through the transparent areas on the code strip and fully blocked by the opaque areas.
Over time, normal operation of the device in which the optical encoder is located results in the collection of dust, ink spray and other contaminants on the code strip. An unclean code strip changes the amount of light received by the detector, resulting in erroneous, and eventually useless data. In an effort to overcome the problems associated with unclean code strips designers have developed wipers which can be assembled on a carriage or other associated moving part, and are used to clean contaminants off the codestrip. These wipers are cleaned periodically at service stations within the device. As this method of keeping the code strip clean is not perfect, the transparency of the code strip continually degrades. Designers study this degradation of transparency, and using empirical data, provide means to raise the current to the light source after specific intervals of operation. The current to the light source is increased in predetermined increments up to a maximum. The life span of the optical encoder depends on this compensation process.
Compensation on a predetermined schedule is an inefficient means of maintaining the integrity of the signal. From the time the code strip is dirty until the scheduled cleaning or until the scheduled increase in the brightness of the light source, the signal created by the optical encoder is distorted. A scheduled cleaning or a scheduled increase in the brightness of the light source which occurs before the transparency of the code strip is actually degraded is unnecessary. Any compensation mechanism employed too soon or too late is inefficient.